Cathode-getter materials for sputter-ion pumps

ABSTRACT

An improved cathode-getter member for utilization in a sputterion type pump for providing effective pumping of a wide range of gases including hydrogen. The cathode-getter member consists of one or more of the refractory metals capable of forming nongaseous hydrides such as zirconium, thorium, titanium, tantalum, niobium and vanadium with an additional constituent consisting of one or more of the following elements, aluminum, silicon and beryllium.

United States Patent [151 3,684,40 l Singleton [451 Aug. 15, 1972 [54] CATHODE-GETTER MATERIALS FOR 3,240,569 3/ 1966 Buescher ..313/346 SPUTTER-ION PUMPS 3,427,491 2/ 1969 Mizuno et a1 ..313/346 Inventor: J H. si g n Pa. Brubaker [73] Assignee: Electric Corporation, P E i -R bert M. Walker Plttsburgh, Pa. Attorney-F. H. Henson and c. F. Renz [22] Filed: Nov. 17, 1970 ABSTRACT [21] Appl. No.: 90,259 I An Improved cathode-getter member for utilization m a sputter-ion type pump for providing effective pump- [52] U.S. Cl ..4l7/49, 3 13/346 ing f aywide range f gases including hydrogen. The [51] Int. Cl ..F04b 37/02, H01 1/14, H01 19/06 cathode getter member consists of one or more of the [58] Fleld of Search .....417/48, 49, 51, 313/346, 338 refractory metals capable of forming non gaseous 56 R f hydrides such as zirconium, thorium, titanium, tan- 1 talum, niobium and vanadium with an additional con- UNITED STATES PATENTS stituent consisting of one or more of the following elements, aluminum, silicon and beryllium. 3,327,930 6/ 1967 Vandershce ..417/49 3,229,147 l/ 1966 Affleck ..313/346 X 5 Claims, 1 Drawing Figure l2 l8 l8 PATENTEDAus 15 mm ////////////f// If! INVENTOR WITNESSES CATHODE-GETTER MATERIALS FOR SPUTTER- ION PUMPS BACKGROUND OF THE INVENTION This invention relates to an improved cathode for a sputter-ion pump. The general operation of a sputter ion pump is the establishment of a magnetically confined electrical discharge in and around a space between a cathode and an anode. Electrons are accelerated toward the anode and travel in a tortuous path as a result of the magnetic field and ionize the gas to be pumped. These ions are then accelerated by the potential between the anode and cathode and bombard the cathode causing the removal or sputtering of cathode material. The pumping action of this type of vacuum pump depends on several phenomena. The

pumping of hydrogen in a sputter-ion pump is less efficient than many of the gases normally found such as nitrogen. The difference in efficiency is a consequence both of low ionization probability of the hydrogen, so that fewer ions are produced for a given electron density in the pump, and also of the low sputtering yield of thecathode material by the light hydrogen molecules. As a result of the low sputtering yield, the pumping of hydrogen must occur almost entirely by ion burial in the cathode unless additional sputtering of the cathode occurs as a consequence of the presence of other, heavier molecules in the gas being pumped. The diffusion of the hydrogen into the cathode, so as to maintain the hydrogen content of the surface layer at less than the saturation level, is thus a critical factor in the pumping speed of a sputter-ion pump. The diffusion of hydrogen from the surface of titanium and tantalum cathodes, which are commonly employed in sputter-ion pumps, is relatively slow, and, consequently, is a rate determining factor in the pumping mechanism.

The pumping speed for hydrogen in a sputter-ion pump is commonly claimed to be substantially higher than the normally rated speed. These high speeds are usually of a transient nature except when the hydrogen is of high purity and contains only a small fraction of reactive gases such as nitrogen, oxygen and carbon monoxide. For example, if the pumping speed of a diode pump with titanium cathodes has been increased above the nominal value by a factor of two, using the technique described by others of pumping pure hydrogen at a pressure greater than Torr, the subsequent introduction of nitrogen into the gas which is being pumped, so as to give an impurity level of less than 1 percent by pressure at the pump causes the pumping speed to revert to approximately the nominal level.

At pressures below 10- Torr, the hydrogen pumping speed of a sputter-ion pump normally becomes very small and under some circumstances, hydrogen is actually evolved. Hydrogen is normally the principal component of the residual gas in metal systems so that the poor pumping characteristics of sputter-ion pumps for this gas results in a much higher ultimate pressure than would be calculated from the outgassing rate of the chamber and the nominal pumping speed of the pump at that ultimate pressure. As a consequence of this limitation, sputter-ion pumps are frequently combined with subsidiary pumps, such as titanium sublimation type pump so as to improve the pumping characteristics. Such combinations greatly increase the cost of 0 greatly reduced by the use of suitable refractory metals capable of forming a non-gaseous hydride and mixed with an additional constituent of aluminum, silicon or beryllium. Suitable getter materials are discussed in British Pat. No. 755,804. I

SUMMARY OF THE INVENTION The present invention by providing a suitable cathode getter material for the sputter-ion pump comprised of at least one refractory metal capable of forming non-gaseous hydrides such as zirconium, thorium, titanium, tantalum, niobium and vanadium mixed with one or more of the following elements, aluminum, silicon and beryllium.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing, exemplary of the invention illustrates a sputter-ion pump according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a typical sputter-ion pump 10 is illustrated and incorporates cathodes 14 of the type described herein. The diode pump device includes an evacuated envelope 12 containing a pair of spaced apart disk like cathodes 14 and an intermediate cylindrical or ring type anode 16. The anode l6 and the cathodes 14 are arranged along a common axis. External to the envelope 12, there is positioned a permanent magnet 18 with its pole pieces positioned along the above-mentioned axis so that the lines of force 'of the magnetic field are directed perpendicular to and through the ring anode 16. A potential source 20 such as a battery is provided for applying positive potential of about 2000 volts to the anode 16 with respect to the cathodes l4. Electrons tending to flow to the anode 13 from the cathodes 14 are urged into a spiral path by the presence of the magnetic field generated by the magnets 18 and a collision of these electrons with gas minum. The cathode 14 may be formed by taking a quantity of 84 percent by weight of pulverulent zirconium and 16 percent by weight of pulverulent aluminum. These two materials are mixed and melted in a vacuum.

The resulting alloy may then be used to form the f cathodes 14.

The cathode 14 may be formed of a suitable refractory metal capable of forming non-gaseous hydrides such as zirconium, thorium, titanium, tantalum, niobium and i vanadium in a powdered form mixed with an additional constituent consisting of one or more of the following powdered non-vaporized elements aluminum, silicon or beryllium.

I claim as my invention:

1. A sputter-ion pump for effectively pumping hydrogen over a wide pressure range comprising an enclosure member, an anode provided within said enclosure, a cathode-getter member positioned within said envelope, means for establishing a magnetic field within the region between said cathode-getter member and said anode, said cathode-getter member comprising in combination a. at least one constituent selected from the group of materials that form stable non-gaseous hybrids, and

b. at least one constituent selected from the group consisting of aluminum, silicon and beryllium.

2. The device set forth in claim 1 in which said materials that form stable non-gaseous hydrides are closure member, an anode provided within said enclo-- sure, a cathode-getter member positioned within said envelope, means for establishing a magnetic field within the region between said cathode-getter member and anode, said cathode-getter member comprised of aluminum and zirconium.

S. The pump set forth in claim 4 in which said cathode-getter member is comprised of about 84 percent zirconium and 16 percent aluminum. 

1. A sputter-ion pump for effectively pumping hydrogen over a wide pressure range comprising an enclosure member, an anode provided within said enclosure, a cathode-getter member positioned within said envelope, means for establishing a magnetic field within the region between said cathode-getter member and said anode, said cathode-getter member comprising in combination a. at least oNe constituent selected from the group of materials that form stable non-gaseous hybrids, and b. at least one constituent selected from the group consisting of aluminum, silicon and beryllium.
 2. The device set forth in claim 1 in which said materials that form stable non-gaseous hydrides are selected from the group consisting of zirconium, thorium, titanium, tantalum, niobium and vanadium.
 3. The device set forth in claim 1 including potential means connected across said cathode-getter member and said anode of sufficient potential to generate sufficient ionic bombardment of said cathode-getter member to cause sputtering of the material from said cathode-getter member.
 4. A sputter-ion pump for effectively pumping hydrogen over a wide pressure range comprising an enclosure member, an anode provided within said enclosure, a cathode-getter member positioned within said envelope, means for establishing a magnetic field within the region between said cathode-getter member and anode, said cathode-getter member comprised of aluminum and zirconium.
 5. The pump set forth in claim 4 in which said cathode-getter member is comprised of about 84 percent zirconium and 16 percent aluminum. 